Polyamide polymers are well known in the art. They are generally prepared by the condensation polymerization of a dicarboxylic acid and a diamine or the condensation of a monoaminomonocarboxylic acid which is normally derived from its internal lactam. Examples of such polyamides are nylon 6,6 or nylon-6 which are respectively prepared from hexamethylene diamine - adipic acid mixtures and epsiloncaprolactam. These polyamides are important fiber forming polymers. Examples of other fiber-forming polyamides are nylon -6/6,6 copolymers, nylon-11, nylon-12 and the nonsynthetic polyamides, wool and silk. Fiber-forming polyamides are well known and are normally dyeable with an acid or direct dye.
It is well known to modify polyamides to make them dyeable with a basic dye. Synthetic polyamides may be modified to render them basic dyeable by replacing a portion of the nylon forming monomer with a corresponding molar amount of sulfonated nylon-forming monomer. U.S. Pat. No. 4,579,762; column 3, lines 24-68 and column 4, lines 1-25 discloses various methods for modifying nylon to render it basic dyeable (i.e. dyeable with a basic dye). U.S. Pat. No. 3,389,172 discloses another such modification procedure; see columns 1 to 3 thereof. The preceding references to U.S. Pat. Nos. 4,579,762 and 3,389,172 are incorporated herein by reference. Natural polyamides can be sulfonated to introduce sulfonic acid groups into the polyamide chains.
For the purpose of this description basic dyeable polyamide is termed cationic polyamide or cationic nylon as the case may be. Acid dyeable polyamides or nylon is termed anionic polyamide or anionic nylon as the case may be.
It is possible to weave or tuft polyamide fibers of the anionic and cationic type into a substrate in a predetermined manner to produce a defined pattern. Theoretically it is then possible to dye the mixed anionic/cationic substrate with an acid dye and obtain a substrate wherein only the anionic portion is dyed. Thus a multi-colored pattern is theoretically achieved on the substrate wherein the anionic portion is colored the shade of the acid dye and cationic portion is undyed (white). However, in practice this is not the result. The commonly used monosulfonated acid dyes will severely cross-stain and dye the cationic polyamide portion and when reserving or milling acid dyes are used cross staining and dyeing of the cationic polyamide still occurs.
This invention avoids this cross staining and dyeing of the cationic portion or the substrate. It is now possible with this invention, to obtain maximum multi-color effects. For example, a selected vinyl sulfone dye can be applied in accordance with invention to an anionic/cationic polyamide substrate and the cationic portion will be undyed. Thus, with the invention, it would be possible to obtain a black anionic portion and a white cationic portion with no graying or discoloration of the cationic fibers in the substrate.